The present invention relates to a surface defect detection apparatus for inspecting defects on a surface of a plane or cylindrical matter, and more particularly concerns a surface defect detection apparatus being capable of detecting a rather gentle wavy defect at a high speed.
There has been a known flying spot method to inspect the surface of the plane or cylindrical matter in a non-contact way. In the method, a laser beam is scanned on the moving matter with use of a rotation multi-plane mirror or an oscillation mirror. The light reflected from the matter is different depending on state of the defect. This is used for the inspection.
There are two kinds of defects on the surface of the inspected matter: (1) a wavy defect of relatively gentle roughness and (2) a minute rough defect which causes rough surface. The reflected lights for the wavy defect existing on the surface of the matter and for no defect are shown by a curve n1 of the light reflected from the wavy defect in FIG. 6 and a curve of the light reflected from the good surface in FIG. 5. The center line of the curve of the light reflected from the wavy defect, as seen from the figures, is deviated from the normal reflection direction.
A photo-sensor device can be provided to rightly face the normal reflection direction with the laser beam irradiated to the matter. For the wavy defect, the reflected light will be deviated from the photo-sensor device or made to come in a corner thereof. For the minute rough defect, the laser beam is scattered on the surface of the matter as reflected so that the quantity of the reflected light coming into the photo-sensor-device can be reduced as compared with the normal reflected light (see the curve n2 in FIG. 5).
The two defects (1) and (2) mentioned above may be produced as superimposed on the surface of the matter, or may be independent thereon.
In the inspection of the surface of the matter by the flying spot method, there has been a case that the photo-sensor device can be moved in the scanning direction to receive the light. This, however, takes too much time to do the surface inspection as mechanical movement of the photo-sensor device has to be made.
In contrast to the flying spot method described above, it has been proposed to inspect a surface of a matter in a way that an apparatus has a photo-sensor device having a strip light receiving window fixed for receiving a reflected light of a single scanning and is to move the matter to be inspected. This inspection method allows a whole surface inspection at a high speed.
However, the apparatus can detect the minute rough defect (2) as the quantity of light coming from a defective point is reduced, but is hard to detect the wavy defect (1). The apparatus, therefore, cannot distinguish the wavy defect (1) from the minute rough defect (2).
In view of the foregoing, it is a general object of the present invention to provide a surface defect detection apparatus that can detect the wavy defect (1) at a high speed.